Recovery of the timing of a received digital data signal is necessary in order to demodulate or otherwise utilize the signal. In other words, the sampling in the receiver must be synchronized with the modulation imposed at the transmitter.
Since no spectral component at the timing frequency exists in the signal as it is received, many methods have evolved for creating such a component, or tone, to which a sampling device in the receiver can be synchronized. An example of such a device is disclosed in U.S. Pat. No. 4,064,361 issued to Kustka et al. One embodiment disclosed therein comprises two quadrature channels, each of which is split into a delayed and an undelayed portion. The delayed and undelayed portions in each channel are correlated, or multiplied, and the two channels are recombined to produce the tone bearing signal. However, due to the correlation of the noise in each of the channels, the performance of this device may be unsatisfactory at low SNR. In addition, the delay time must be chosen with knowledge of the carrier frequency, thus severely limiting the range of application of such a device.